Producing high quality holograms by copying

ABSTRACT

The production of a hologram free from undesirable line structures by forming a phase hologram by bleaching an absorption hologram and then copying the phase hologram using a gas discharge tube to radiate the phase hologram with and thus produce a hologram completely free from coarse residual fringes.

9 S R 350 3 e x M V h Len-an 72 lnventors Heinrich Nassenstein 50 FieldofScarch .Q 35013.5; Leverkusen; 355/2 Manfred Kllemann, Schlldgen,Germany [21] Appl. No. 748,635 [56] References Clted [22] Filed July 30,1968 OTHER REFERENCES l Patented 30, 1971 Ramberg, RCA REVIEW v01. 27.Dec. 1966, pp 467 499 1 Asslsnee AfiFA-Gevflert Aktiensesellschm (pp479- 487 relied upon) copy in 350/15 Leverkusen, Germany [32] PriorityAug. 18, 1967 Primary Examzaer-David Schonberg [33] Germany AssistantExaminer-Ronald J. Stern [31] AS6531 Attomey-Connolly and Hutz [54] HIGHQUALITY HOLOGRAMS BY ABSTRACT: The production of a hologram free fromun- 3 Cl l D desirable line structures by forming a phase hologram byguns "wing bleaching an absorption hologram and then copying the phase[5 2] US. Cl 350/3.5, hologram using a gas discharge tube to radiate thephase holo- 355/2 gram with and thus produce a hologram completely freefrom [5 l] Int. Cl G02b 27/00 coarse residual fringes.

PATENTEB HAR30I97I s- 9 INVENTORS; HEINRICH NASSENSTEIN, MANFHEDKLIEMANN.

PRODUCING HIGH QUALITY HOLOGRAMS BY COPYING The present inventionrelates to a method of producing high quality holograms.

Nonnal holograms which are produced by diffraction and interferenceeffects show coarse residual fringes due to dust and dirt, hereinaftercalled undesirable line structures, which reduce the value of thereconstructed picture. Whilst these effects can be reduced bycomplicated measures using highquality optical components, such measuresrestrict choice of the arrangement used for exposing the hologram.

It has now been found that highquality holograms can be produced in asimple manner by first of all producing a phase hologram, which is thencopied. it has surprisingly been established that such a phase hologramcan be copied just as well as a density hologram and that, in thiscopying process, the undesirable line structures, which are stillpresent on the phase hologram as phase structures, are not copied. Thedatacarrying fine interference structure is however transferred to thep), 85 can be seen in the satisfactory reconstruction of the picture orimage on the copy. A copy of macroscopically uniform density is thusobtained which is completely free from the undesirable line structurespresent in the original. This is due to the fact that the copy is not acopy in the conventional sense, but is a holographic copy, i.e. a copyis a hologram of the phase hologram original. The phase hologram used asthe original can be directly produced in a manner known per se byvarious photographic processes or, advantageously, by bleaching outdensity holograms to give phase holograms in a manner known per se. lnanother advantageous development of the method according to theinvention, a gas discharge lamp is used as light source during thecopying. One may use for this purpose, a mercury arc lamp, using afilter for the green mercury line. In addition, one also may use ableached image plane hologram with inline reference pencils as original,i.e. a hologram in which the reference pencil is incident in the opticalaxis, in which case it is advantageous to use an incandescent lamp aslight source for the production of the copy. By using gas dischargelamps and incandescent lamps as light source according to the inventionwith very small coherence length of the light, the formation during thecopying process of the new line structures which are found in thepreviously used methods when working with a laser is avoided.

in the method according to the invention. it is now possible whenexposing the hologram, to exercise a free choice over the arrangement,without need to consider any disadvantageous interference effects. inparticular, the method allows the production of large numbers ofholograms which are completely free from disturbing line structures bycopying from one phase hologram. if so desired. these copies can bereconverted to phase holograms, either by bleaching a density hologramor by another photographic process which is known per se and which leadsdirectly to a phase hologram.

A relevant literature reference is Zeitschrift fuer angewandte Physik,"Vol. 22, lssue l, pages 37-50 (Imageforrning method with reconstructionof the wave field (holography))," (by H. Nassenstein), where theproduction of phase holograms is, for example, described. Thisliterature reference also contains a full record of the pertinentliterature.

Another pertinent article is by E. B. Brumm in Applied Optics, Vol. 5,No. 12, Dec. i966, pages l946-l947 with particular reference to FIG. 1.This is pertinent to the performance of the copying process wherein apreviously produced hologram is copies.

FIG. 1 is a diagrammatic illustrating the radiation from the lamp or gasdischarge tube and the relative positioning of an original phasehologram and a product hologram on a photographic plate.

In H6. 1 a light source is provided which is preferably a gas dischargetube. The light source 1 emits a radiation illustrated by the dot anddash line. The radiation is projected to a phase hologram 2 and afterbeing transmitted through the phase hologram 2 impinges on aphotographic plate 3 on which the product hologram is produced.

We claim: 1. In the method of producing holograms free from coarseresidual fringes the steps of first bleaching an absorption hologram toform a phase hologram, projecting a light beam of short coherence lengthfrom a light source through said phase hologram and subsequentlyimpinging said beam on a photographic plate so as to create aholographic copy of the phase hologram on the photographic plate.

2. ln the method as claimed in claim 1 using a gas discharge tube toproduce the short coherence length light beam.

3. In the method as claimed in claim I using an incan descent lamp assaid light source.

1. In the method of producing holograms free from coarse residualfringes the steps of first bleaching an absorption hologram to form aphase hologram, projecting a light beam of short coherence length from alight source through said phase hologram and subsequently impinging saidbeam on a photographic plate so as to create a holographic copy of thephase hologram on the photographic plate.
 2. In the method as claimed inclaim 1 using a gas discharge tube to produce the short coherence lengthlight beam.
 3. In the method as claimed in claim 1 using an incandescentlamp as said light source.